The present invention relates to drafting equipment with small double belts for spinning machines with a fiber bundling zone which follows a pair of output rollers and is followed by a pair of delivery rollers. Drafting equipment of this type is described in DE 43 23 472 (U.S. Pat. No. 5,600,872). Therein a pneumatic compression device is installed between the pair of output rollers and the pair of delivery rollers, said compression device being provided with a small perforated belt and a suction device extending on the side of the small belt away from the fiber sliver and aspiring air through the fiber sliver.
Very good results are achieved with this known device with respect of gathering together and bundling of the fibers, so that a smooth yarn with considerably improved resistance to tearing is spun. It was shown, however, that the pneumatic compression device has relatively high air consumption. When using the conventional traversing apparatus, it may furthermore occur that border fibers are no longer seized securely because they are either outside the perforation zone, or because the negative pressure is not sufficiently strong to bundle them. An enlargement of the perforation zone not only requires more air but decreases the gathering together of the fibers. Increased negative pressure also required more suction capacity. It is however also important for the obtention of uniform spinning results that the optimal state of the drafting equipment, in particular of the compression device, be maintained.
In the known device, a small belt is used without fabric insert in order to release the fibers at the outlet of the delivery roller which had been sucked into the perforation by their ends. These small belts without fabric inserts do not last long.
It is a principal object of the present invention to avoid the described disadvantages and to improve the compression effect of the known device while reducing the suction capacity. Additional objects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.
The invention is based on recognition of the fact that only a relatively short distance is necessary for the bundling of the fiber sliver regardless of the staple length of the fibers. The maintenance of the suction air stream as far as into the area of the nip of the delivery cylinder merely serves to maintain the bundling of the fiber sliver up to the entry into the pair of delivery cylinders.
The shortening of the suction zone according to the teaching of this invention results in considerably reduced air consumption and heightened compression effect. Fibers which may have been diverted during transportation are again bundled by further compression in the immediate area before the entry of the fiber sliver into the nip of the delivery cylinder.
By connecting the perforation openings by one or several grooves, a mechanical holding of the bundled fibers is achieved so that the fibers are kept in their bundled position even without suction effect. Furthermore, by providing several grooves, the small belts can be used universally with fiber slivers of different thicknesses.
By using perforation openings with dimensions perpendicular to the direction of fiber movement greater than parallel to the direction of fiber movement, the fiber sliver is safely brought together also during traversing. A certain rough gathering together results, so that the perforation can be kept smaller for the actual compression and so that not only savings in air, but also a closer gathering together of the roving is achieved.
In order to always maintain the effect of the pneumatic compression device at an optimal level, it has proved to be necessary to clean it from time to time. This is especially necessary with a lowered negative pressure. This can be carried out easily by a device wherein the compression device is equipped with a small perforated belt and with a suction device which extends on the side of the belt away from the fiber sliver and which sucks air through the fiber sliver, and also including a blowing air channel that lets out across from the outlet of the suction air channel in a housing-shaped belt cage. This embodiment makes also automation, e.g. in connection with thread piecing, possible. Finally, with the present invention, small belts with long life can be used and reliable release of fibers caught at the outlet from the delivery cylinder can nevertheless be achieved.
An embodiment wherein the perforations of the compression device belts is free of burrs makes it possible to avoid a clogging of the perforation by dust etc. and thereby to avoid lowering of the optimal suction effect.
Further details of the invention are described through the drawings.